The computer networks used by fourth-generation (4G) mobile terminals include radio sub-networks, sometimes referred to by the abbreviation RAN (“Radio Access Network”), which are connected to an interconnection network, also referred to as a CSN (“Connectivity Service Network”), the CSN being able to be connected to the Internet. A fourth-generation mobile terminal is identified by an IP (“Internet Protocol”) address that allows it to receive and transmit data across the entire computer network. The mobile terminal is within the coverage area of an antenna station, also referred to as a base station. An RAN is formed by a set of base stations, the coverage areas of which complement one another to cover an area. The data are transmitted between the mobile terminal and the base station in the form of radio waves, then the base station transmits the data, generally via cables or optical fibers, to a gateway serving as the interface between an RAN and a CSN. As a general rule, a plurality of base stations are controlled by the same gateway. A gateway of this type performs a variety of functions, notably packet filtering, quality of service management, user authentication and base station control. For the sake of simplification, the gateway term ASN-GW (“Access Service Network Gateway”) will be used below to refer to the gateways present in the WiMax networks; however, this term must not be interpreted in a limiting manner, since the invention can apply to all types of fourth-generation networks.
When the mobile terminal moves and leaves the zone covered by a first base station within the coverage area of which it was situated, communications are provided by a second base station whose coverage area is adjacent to the first. If the second base station is connected to the same ASN-GW gateway as the first base station, the term micro-mobility is used. In the case where the second base station is connected to an access ASN-GW gateway different from the first ASN-GW gateway, the term macro-mobility is used. The present invention relates more particularly to continuity of the management of communications in the context of the micro-mobility of the mobile terminals.
The communications sessions management allows a call negotiation protocol to be run between two users, aiming to ensure that these two users have the means to dialogue with one another before a call is set up (for example setting up a coherent encoder/decoder at both ends of the line). This management can be carried out using a protocol operating on a client-server architecture. For example, the SIP protocol is based on an interworking between a client software module installed on a terminal and an SIP server present in the CSN.